PROSTHESIS
The invention relates to a femoral component (2) of a knee prosthesis. The component comprises a curved outer surface (4) for bearing against a tibial component. Said curved outer surface includes a posterior end and an anterior end. The curved outer surface includes an area (A) which extends from a first position closer to the posterior end to a second position closer to the anterior end, wherein said area (A) includes no parting line.
This invention relates to a prosthesis and particularly, although not exclusively, relates to a knee prosthesis. Preferred embodiments relate to a femoral component of a knee prosthesis, a combination and assembly which includes said femoral component and a method of making a femoral component.
Various materials have been proposed and/or used for the femoral and tibial components of knee prostheses. For example, the components may be made from various combinations of metal, ceramics and polymers. In the last ten years, more interest has been focussed on all-polymer knee prostheses. For example, US2009/0164023 (Devine) described artificial joints, for example knee joints, which include both bearing surfaces made from composite materials which comprise a polyaryletherketone polymer (e.g. polyetheretherketone i.e. PEEK) and carbon fibre. The composite materials are said to have improved wear compared to other combinations based on metal bearing on metal, metal bearing on polymer or one specified polymer bearing on another specified polymer.
US2010/0312348 (Wang) discloses an orthopaedic prosthetic joint which may be a knee joint. The joint is said to comprise a first bearing surface made of a polyaryletherketone (PAEK), for example PEEK, and a second joint component having a second bearing surface made of a polymer which is softer than the PEEK. In preferred embodiments, the second polymer is an ultra-high molecular weight polyethylene (UHMWPE).
Both US2009/0164023 and US2010/0312348 suggest the bearing surfaces may be provided in various ways. For example US2009/0154023 suggests components may be made substantially entirely from the composite materials described or only a bearing surface may be formed from the composite materials, for example by capping or coating a layer of composite material on a precursor, for example defining a femoral head, which may be made from metal or ceramic. No further detail on how the components may be made is provided.
Similarly, US2010/0312348 describes, for example, a PEEK bearing and states this may be a stand-alone PEEK component or a PEEK layer could be coated, moulded or grafted onto another solid or porous polymer or polymeric composite; or onto a solid or porous metallic or ceramic substrate. Again, other than generic statements, no further detail or specific embodiments on how the components may be made is provided.
Applicant has appreciated that techniques that may be used for manufacturing components of knee prostheses, may affect wear and longevity of the prostheses in use. It is an object of the present invention to address this problem.
Preferred embodiments aim to provide an advantageous femoral component of a knee prosthesis. Preferred embodiments aim to provide an advantageous knee prosthesis.
According to a first aspect of the invention, there is provided a femoral component of a knee prosthesis, said component comprising a curved outer surface for bearing against a tibial component, said curved outer surface including a posterior end and an anterior end, wherein said curved outer surface includes an area (A) which extends from a first position closer to the posterior end to a second position closer to the anterior end.
Preferably, said area (A) includes no parting line.
Area (A) preferably includes no remnant of a parting line. A parting line (or seam) suitably comprises a line formed on an injection moulded part, during injection moulding, which witnesses where two mould parts met. On ejection from a mould, a parting line may be in the form of a thin line extending from a surface of the injection moulded part. The line may typically have a height of 0.02-0.03 mm. As described, area (A) preferably does not include any parting line and preferably does not include any remnant of a parting line. Thus, area (A) preferably does not include any parting line and never included any parting line—i.e. a parting line has not been removed to define any part of area (A). Thus, area (A) suitably is an area of said curved outer surface of said femoral component which has not been treated to remove or reduce any parting line. This may be advantageous since no machining (or the like) needs to be used to define area (A), thereby avoiding production of machining marks or contamination of area (A) by metal (or other) particles detached from a machine tool, for example a metal machine tool. Furthermore, it may reduce manufacturing cost by avoiding a potentially extra precision machining step in producing the femoral component.
The shape of area (A) is preferably wholly defined by a tool surface used in its manufacture, for example by a surface of an injection moulding tool. Area (A) is preferably a wholly as-moulded surface. Other than being cleaned and/or sterilised, it is preferably not a surface which has been subjected to any treatment which may change its shape.
Preferably, said femoral component includes said curved outer surface for bearing against a tibial component and a flexion/extension axis, suitably determined as described in ISO14243-1:2009(E) at 3.6.
Area (A) of said curved outer surface suitably subtends an angle (e.g. a maximum angle) of at least 150°, preferably at least 160°, with the flexion/extension axis. That is, an angle defined between said first and second positions of said area and said flexion/extension axis is preferably as stated. The angle subtended is suitably defined in a plane which is suitably perpendicular to the flexion/extension axis. The plane may extend through a condyle of the femoral component. Said angle is suitably 180° or less.
Area (A) suitably comprises an area of the curved outer surface which is arranged to contact, pivot and/or roll over a surface (herein a “tibial surface”) of a tibial component in normal use to define at least part of a knee prosthesis. The femoral component may be arranged to pivot and/or roll over the tibial surface so the femoral component can pivot through an angle of at least 140°, for example at least 150° or at least 155°, with only area (A) of said femoral component (and suitably no other area of the femoral component) contacting the surface of the tibial component. Thus, said femoral component is preferably arranged to pivot through an angle of at least 140°, for example at least 150° or at least 155°, without any parting line and/or without any remnant of a parting line contacting the tibial surface. It may be arranged to pivot through an angle of less than 180°, for example less than 175° or less than 170°.
As described, area (A) suitably comprises an area of the curved outer surface which is arranged to contact and roll over a tibial surface in use. Movement of area (A) on a tibial surface may be affected by the shape of the tibial surface. To address this, features of the femoral component may be assessed in conjunction with a planar surface, for example, as described in Assessment (A) hereinafter. Preferably, the femoral component is arranged such that area (A) can contact a planar surface and be pivoted through an angle of at least 140° (preferably through at least 150° or 155°) without any parting line, remnant of a parting line or area from which a parting line has been removed, contacting the planar surface. It may be arranged to pivot through an angle of less than 180°, for example less than 175° or less than 170°.
The femoral component may be subjected to the following assessment:
-
- (i) contact a planar surface with area (A) of said curved outer surface of said femoral component, wherein area (A) suitably represents an area of the curved outer surface which is arranged to contact and roll over a tibial surface in normal use; (ii) pivoting (suitably about an axis parallel to the planar surface) the femoral component so that area (A) rolls over the planar surface between first and second extreme positions, wherein during said pivoting movement of the femoral component between said extreme positions, no parting line, remnant of a parting line and/or other area from which a parting line has been removed contacts the planar surface; and (iii) assessing the maximum angle through which the femoral component can be pivoted between said first and second extreme positions.
Preferably, the femoral component can be pivoted through an angle of at least 140°, preferably at least 145°, more preferably at least 150°, especially at least 155°, without any contact of a parting line, remnant of a parting line and/or other area from which a parting line has been removed with the planar surface. Said angle through which said femoral component may be pivoted as aforesaid may be less than 180°, less than 175° or less than 170°.
Said first extreme position of the femoral component may represent an extreme of flexion of the femoral component (e.g. wherein an area of the femoral component adjacent its posterior end contacts the planar surface, for example as shown in
Said second extreme position may represent an extreme of extension of the femoral component, for example as shown in
During the movement of the femoral component from said first extreme position to said position wherein the posterior end contacts the planar surface (e.g. clockwise from the position shown in
During the movement of the femoral component from the second extreme position to said position wherein the anterior end contacts the planar surface (e.g. anti-clockwise from the position shown in
The ratio of LD2 divided by LD1 may be at least 5, for example at least 7, 9 or 12.
Said femoral component may include a parting line, a remnant of a parting line or an area from which a parting line has been removed. When it includes a parting line, said parting line may have a height of less than 0.05 mm, for examples less than 0.03 mm. The height may be at least 0.005 mm, for example at least 0.01 mm. The height is typically 0.025 mm.
Said femoral component may include a parting line, a remnant of a parting line or an area from which a parting line has been removed in a region of said curved outer surface of the femoral component which is outside area (A) and is arranged between area (A) and a posterior end of the femoral component.
Said femoral component may include a parting line, a remnant of a parting line or an area from which a parting line has been removed in a region of said curved outer surface of the femoral component which is outside area (A) and is arranged between area (A) and an anterior end of the femoral component.
Said femoral component preferably includes first and second condyles which are suitably arranged to engage and/or roll over the tibial surface and/or the planar surface described during assessment of the femoral component.
Said femoral component preferably includes an undercut region. Said undercut region is preferably defined in a surface of said femoral component which faces in a direction which is opposite to the direction in which said outer surface faces. Said undercut region is preferably an internal undercut. Said undercut region is preferably arranged to define a cement pocket in said femoral component for retaining cement which may be used to facilitate securement of the femoral component to a femur during implantation. Said cement pocket may have a depth of at least 0.5 mm, more preferably at least 1 mm. The cement pockets may be less than 8 mm.
Said femoral component preferably includes multiple undercut regions each of which may have any feature of said undercut region described. Said femoral component suitably includes a series of ribs (which may define one or more undercut regions) defined in said surface of the femoral component which faces in a direction which is opposite to the direction in which said outer surface faces. Preferably, the ribs are arranged mutually parallel to each other, having straight sides. The ribs are equi-distantly spaced. Preferably, the ribs run parallel to the flexion extension axis.
Said femoral component preferably includes undercut regions associated with anterior and/or posterior flanges thereof.
Said femoral component preferably comprises an injection moulded component. Said femoral component is preferably made substantially entirely by injection moulding. Said femoral component preferably comprises a polymeric material, for example a thermoplastic polymeric material. At least 50 wt %, suitably at least 70 wt %, preferably at least 80 wt %, more preferably 90 wt %, especially at least 95 wt %, for example at least 99 wt %. of said femoral component is made from thermoplastic polymeric material, for example from a first polymer as herein described.
Said curved outer surface of said femoral component is preferably formed in an injection moulding process. Said curved outer surface preferably comprises a polymeric material, for example a thermoplastic polymeric material. At least 50 wt %, suitably at least 70 wt %, preferably at least 80 wt %, more preferably 90 wt %, especially at least 95 wt %, for example at least 99 wt %. of said curved outer surface is made from thermoplastic polymeric material, for example from a first polymer described herein.
Said femoral component is preferably a solid body. It is preferably monolithic. It is preferably made in one piece by injection moulding.
Said first polymer is preferably a polyaryletherketone. A preferred polyaryletherketone has a repeat unit of formula (I)
-
- where t1 and w1 independently represent 0 or 1 and v1 represents 0, 1 or 2.
Said polyaryletherketone suitably includes at least 90, 95 or 99 mol % of repeat unit of formula I. Said polyaryletherketone suitably includes at least 90, 95 or 99 wt % of repeat units of formula I.
Said polyaryletherketone preferably consists essentially of a repeat unit of formula I. Preferred polymeric materials comprise (especially consist essentially of) a said repeat unit wherein t1=1, v1=0 and w1=0; t1=0, v1=0 and w1=0; t1=0, w1=1, v1=2; or t1=0, v1=1 and w1=0. More preferred comprise (especially consist essentially of) a said repeat unit wherein t1=1, v1=0 and w1=0; or t1=0, v1=0 and w1=0. The most preferred comprises (especially consists essentially of) a said repeat unit wherein t1=1, v1=0 and w1=0.
In preferred embodiments, said first polymer is selected from polyetheretherketone, polyetherketone, polyetherketoneetherketoneketone and polyetherketoneketone. In a more preferred embodiment, said first polymer is selected from polyetherketone and polyetheretherketone. In an especially preferred embodiment, said first polymer material is polyetheretherketone.
Said polyaryletherketone may have a Notched Izod Impact Strength (specimen 80 mm×10 mm×4 mm with a cut 0.25 mm notch (Type A), tested at 23° C., in accordance with ISO180) of at least 4 KJm−2, preferably at least 5 KJm−2, more preferably at least 6 KJm−2. Said Notched Izod Impact Strength, measured as aforesaid, may be less than 10 KJm−2, suitably less than 8 KJm−2. The Notched Izod Impact Strength, measured as aforesaid, may be at least 3 KJm−2, suitably at least 4 KJm−2, preferably at least 5 KJm−2. Said impact strength may be less than 50 KJm−2, suitably less than 30 KJm2.
Said polyaryletherketone suitably has a melt viscosity (MV) of at least 0.06 kNsm−2, preferably has a MV of at least 0.09 kNsm−2, more preferably at least 0.12 kNsm−2, especially at least 0.15 kNsm−2. Advantageously, the MV may be at least 0.35 kNsm−2 and especially at least 0.40 kNsm−2. An MV of 0.45 kNsm−2 has been found to be particularly advantageous in the manufacture of accurate, strong frameworks.
Unless otherwise stated herein, MV is measured using a Bohlin Instruments RH2000 capillary rheometer according to ISO 11443 operating at 340° C. and a shear rate of 1000 s−1 using a 0.5 mm (capillary diameter)×8.0 mm (capillary length) die with entry angle 180° C. Granules are loaded into the barrel and left to pre-heat for 10 minutes. The viscosity is measured once steady state conditions are reached and maintained, nominally 5 minutes after the start of the test. Said polyaryletherketone may have a MV of less than 1.00 kNsm−2, preferably less than 0.5 kNsm−2. Said polyaryletherketone may have a MV in the range 0.09 to 0.5 kNsm−2, preferably in the range 0.14 to 0.5 kNsm−2, more preferably in the range 0.4 to 0.5 kNsm−2.
Said polyaryletherketone may have a tensile strength, measured in accordance with ISO527 (specimen type 1b) tested at 23° C. at a rate of 50 mm/minute of at least 20 MPa, preferably at least 60 MPa, more preferably at least 80 MPa. The tensile strength is preferably in the range 80-110 MPa, more preferably in the range 80-100 MPa.
Said polyaryletherketone may have a flexural strength, measured in accordance with ISO178 (80 mm×10 mm×4 mm specimen, tested in three-point-bend at 23° C. at a rate of 2 mm/minute) of at least 50 MPa, preferably at least 100 MPa, more preferably at least 145 MPa. The flexural strength is preferably in the range 145-180 MPa, more preferably in the range 145-184 MPa.
Said polyaryletherketone may have a flexural modulus, measured in accordance with ISO178 (80 mm×10 mm×4 mm specimen, tested in three-point-bend at 23° C. at a rate of 2 mm/minute) of at least 1 GPa, suitably at least 2 GPa, preferably at least 3 GPa, more preferably at least 3.5 GPa. The flexural modulus is preferably in the range 3.5-4.5 GPa, more preferably in the range 3.5-4.1 GPa.
Said polyaryletherketone may be amorphous or semi-crystalline. It is preferably crystallisable. It is preferably semi-crystalline. The level and extent of crystallinity in a polymer is preferably measured by wide angle X-ray diffraction (also referred to as Wide Angle X-ray Scattering or WAXS), for example as described by Blundell and Osborn (Polymer 24, 953, 1983). Alternatively, crystallinity may be assessed by Differential Scanning Calorimetry (DSC).
The level of crystallinity of said polyaryletherketone may be at least 1%, suitably at least 3%, preferably at least 5% and more preferably at least 10%. In especially preferred embodiments, the crystallinity may be greater than 25%. It may be less than 50% or less than 40%. The main peak of the melting endotherm (Tm) of said polyaryletherketone (if crystalline) may be at least 300° C.
Said femoral component is preferably sterile. Same femoral component is preferably provided in a sterile package.
According to a second aspect of the invention, there is provided a combination for a knee prosthesis, the combination comprising a femoral component and a tibial component, wherein said femoral component includes a curved outer surface for bearing against a surface (herein a “tibial surface”) of the tibial component. Preferably, the femoral component is arranged to roll over the tibial surface through an angle of at least 140°, preferably at least 145°, more preferably at least 150°, wherein during such movement no parting line (e.g. which may be part of said curved surface of the femoral component) contacts the tibial surface. Said rolling movement of the femoral component suitably represents the normal and/or intended movement of the femoral component relative to the tibial component—that is, the normal and/or intended movement when the combination is implanted in a human body. Preferably, during such movement, no parting line (e.g. which is part of said curved surface of the femoral component), remnant of a parting line, (e.g. which is part of said curved surface of the femoral component) or area (e.g. which is part of said curved surface of the femoral component) from which a parting line has been removed, contacts the tibial surface.
Said angle may be less than 180°, less than 175° or less than 170°.
The femoral component may be arranged to roll through an angle up to at least 150° or up to at least 180° without any parting line, remnant of a parting line or area from which a parting line has been removed contacting the tibial surface. Said femoral component may be arranged to roll on the tibial surface between a first extreme of movement (e.g. wherein, when implanted, the knee prosthesis is at one extreme of normal flexion) and a second extreme of movement (e.g. wherein, when implanted, the knee prosthesis is at one extreme of normal extension) without any contact with the tibial surface of any parting line, remnant of a parting line or area from which a parting line has been removed. By avoiding any such contact with the tibial surface during normal flexion and normal extension of the knee prosthesis, wear on the tibial surface (which in a preferred embodiments is softer than said curved outer surface) may be minimised.
Said femoral component of the second aspect may have any feature of the femoral component of the first aspect.
Said tibial component preferably comprises an injection moulded component. Said tibial component is preferably made substantially entirely by injection moulding. Said tibial component preferably comprises a polymeric material, for example a thermoplastic polymeric material. At least 50 wt %, suitably at least 70 wt %, preferably at least 80 wt %, more preferably at least 90 wt %, especially at least 95 wt % of said tibial component is made from thermoplastic polymeric material, for example from a second polymer described herein.
Said tibial surface of said tibial component is preferably formed in an injection moulding process. Said tibial surface preferably comprises a polymeric material, for example a thermoplastic polymeric material. At least 50 wt %, suitably at least 70 wt %, preferably at least 80 wt %, more preferably at least 90 wt %, especially at least 95 wt % of said tibial surface is made from thermoplastic polymeric material, for example from a second polymer described herein.
Said tibial component is preferably a solid body. It is preferably monolithic. It is preferably made in one-piece by injection moulding.
Said femoral component preferably comprises a first polymer as described and said tibial component comprises a second polymer as described. Preferably, said first polymer is harder than said second polymer.
Unless otherwise stated herein, the relative hardness of the materias of said first and second polymers may be assessed by the Ball Indentation method described in ISO 2039-1: 2001.
A hardness ratio may be defined as the hardness of the first polymer divided by the hardness of the second polymer. The hardness ratio may be at least 2, 3, 4, 5 or 6. It may be less than 10, 9 or 8. It is suitably in the range 4 to 9.
Said first polymer may be a polyaryletherketone (PAEK), as described. Said second polymer may be a polyolefin, for example polyethylene, a polyurethane or a polyamide. Said second polymer is preferably polyethylene. Said polyethylene may be crosslinked. It is preferably crosslinked, for example by irradiation. It may comprise UHMWPE. Preferably, it comprises UHMWPE which has been crosslinked at least three times by irradiation. It may comprise X3™ UHMWPE of Stryker Corporation, crosslinked as described in U.S. Pat. No. 7,517,919.
According to a third aspect of the invention, there is provided an assembly comprising a femoral component bearing against a tibial component, said femoral component and/or tibial component being as described in the first and/or second aspects.
According to a fourth aspect of the invention, there is provided a method of making a femoral component according to the first aspect and/or second aspect which comprises injection moulding a thermoplastic polymeric material, for example comprising said first polymer, as described according to said first aspect, thereby to form said femoral component.
According to a further aspect of the invention, there is provided a tooling apparatus for moulding a femoral component, the tooling apparatus comprising a mould for injection moulding the femoral component, the mould having a first element, a second element, a third element, and at least one up and away element, wherein the mould is operable such that parting lines are formed at locations on the surface of the component which do not obstruct use, or cause damage to a corresponding mating surface.
Said femoral component suitably includes a curved outer surface for bearing against the tibial component, wherein said curved outer surface includes a posterior end and an anterior end, wherein said curved outer surface includes an area (A) which extends from a first position close to the posterior end to a second position closer to the anterior end, wherein during injection moulding of said thermoplastic polymeric material no parting line is produced within area (A). During said injection moulding, a parting line may be produced on said curved outer surface outside area (A). For example, a parting line may be produced, on said curved outer surface, between area (A) and a posterior end of the femoral component; and/or a parting line may be produced, on said curved outer surface, between area (A) and an anterior end of the femoral component.
The invention extends to a method of providing a knee prosthesis, the method comprising implanting a femoral component according to the first aspect and/or as described in the second and/or third aspects into a human body. The method may comprise implanting a tibial component as described.
Any feature of any aspect of the invention or embodiment described herein may be combined with any other feature of any aspect of an invention or embodiment described herein mutatis mutandis.
Specific embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
In the Figures, the same or similar parts are annotated with the same reference numerals.
A femoral component 2 (shown in
The parting lines 10, 12, 14 are positioned so the femoral component 2 can move between its extreme positions during flexion and extension (i.e. move through approximately 160°) without parting lines 10, 12, 14 (or for the avoidance of doubt any parting line associated with any part of the femoral component) contacting the articulation surface of the tibial component. Consequently, the only regions of the femoral component which contact the tibial component are “as-moulded” surfaces of the femoral component. Such surfaces can be moulded to have a low Ra. As-moulded articulation surfaces are preferred compared to surfaces which may be polished or otherwise treated to adjust their Ra (or remove parting lines or other undesirable features) since there is a risk, with any post-treatment, of articulation surfaces being contaminated, for example with metal from a tool used to effect a treatment or otherwise damaged during the process. In addition, avoiding post-treatment as described simplifies the manufacturing process for the femoral component which may make it quicker, easier and cheaper. Further details are provided below.
An internal face 16 of femoral component 2 includes respective undercut regions 18, 20 (
Spaced apart projecting conical stems 22 extend inwardly away from the internal face 16, the stems being arranged to engage corresponding sockets formed in a patient's femur. In some embodiments, such stems may be omitted or may be a shape other than conical.
Referring to
The second posterior parting line 12 on the second condyle is substantially a mirror image of the first posterior parting line 10 and the above description of the first posterior parting line applies to the second posterior parting line mutatis mutandis.
An opening 50 between the first and second condyles 6, 8 defines an intercondylar notch arranged to receive a stem 52 (
As shown in
As described, the femoral component is able to roll and/or rotate through a significant angle (e.g. 160° or more) over a surface of a tibial component without any parting line (e.g. parting lines 10, 12, 14) contacting the tibial component. Thus, potential wear on the tibial component by such parting lines is avoided.
Assessment (A) below provides a general method with reference to
Assessment (A)—Assessing Extent of Movement of Femoral Component Over a Planar Surface without a Parting Line on the Femoral Component Contacting the Planar Surface
Referring to
Next, the femoral component is pivoted and/or rolled linearly across the surface to the position illustrated by arrow B. It may suitably be moved from position A to position B about axis of rotation 90 of the femoral component which may be determined in accordance with ISO14243-1:2009(E). In position (B), component 2 is arranged so parting line 14 just avoids contact with the surface 86. Thus, position (B) represents another extreme position of the femoral component 2, wherein parting lines are very close to but do not contact the surface 86.
The angle through which femoral component moves between positions (A) and (B) can be assessed. In
A femoral component and tibial component of a knee assembly for implantation are selected. The extent of movement can be assessed by assembling the components in vitro as shown in
Thus, it should be appreciated that, advantageously, the femoral component can move through approximately up to 170° without any parting line on the femoral component contacting and potentially increasing the wear upon the tibial component. Thus, an assembly as described may have improved wear compared to assemblies which include parting lines at other positions on the femoral component.
It will be appreciated from the embodiments described that at angles greater than the normalized femoral rotation angle or the practical femoral rotation angle (e.g. when the femoral component is rotated beyond the first and second positions described) a parting line on the femoral component would contact the surface 86 (in Assessment A) or the surface of the tibial component (in Assessment B). However, this is not detrimental since the femoral component is not intended to be rotated beyond the first and second positions described. Nonetheless, by retaining a parting line produced in the manufacture of the femoral component as described, the femoral component may be more efficiently manufactured (since no additional parting line removal step is required) and the femoral component can be used substantially “as moulded”, without the bearing surface of the femoral component being polished or otherwise treated to adjust its surface roughness, thereby obviating the risk of contaminating or damaging the articulation surface of the tibial component.
The femoral component 2 is injection moulded using virgin polyetheretherketone (PEEK) which may be PEEK-OPTIMA (Trade Mark), a long-term grade polyetheretherketone with a melt-viscosity of approximately 0.45 KNsm−2, obtainable from Invibio Limited, UK.
The tibial component 9 is made from ultra-high molecular weight polyethylene (UHMWPE) which is softer than the PEEK. Consequently, steps are taken as described herein to minimise wear on the UHMWPE tibial component by the harder PEEK femoral component.
The position of parting lines (and areas which have no parting line) on the femoral component 2 has been described above. Such a femoral component 2 may be manufactured by injection moulding as hereinafter described with reference to
Referring to
The shell of the mould is arranged to define the outer surface 4 of the femoral component and the parting regions 10, 12, 14.
The second element 94 of the mould is arranged to define the entirety of the outer surface 4 of the femoral component which is arranged between parting lines 10, 12, 14. To this end, element 94 includes shaped surface 102 and first and second end faces 104, 106 which extend substantially parallel to one another. The shaped surface of the mould curves through an angle of about 180° to define the outer surface of the femoral component arranged between parting lines 10, 12, 14.
First element 92 cooperates with the second element 94 to define a first split line 108. To this end, first element 92 includes a shaped surface 110 and first and second end faces 112, 114. The first end face 112 abuts the end face 104 and defines part of the split line 108. The shaped surface 110 of element 92 curves through an angle of about 80° between its first and second end faces 112, 114,
The element 92 cooperates with first up and away element 98 to define a second split line 116 adjacent the proximal anterior flange of the femoral component.
Third element 96 comprises a central portion 97 located between said elements 98 and 100, and an arm portion 99. The arm portion 99 is joined to the central portion 97 such that movement of element 96 causes simultaneous movement of said portions 97 and 99. The arm portion 99 cooperates and makes face to face contact with second end face 106 of outer element 94 to define respective split lines 118, 120 adjacent superior posterior condyles of the femoral component 4.
The first, second and third up and away elements 96, 98, 100 cooperate to define the internal face 16 of the femoral component including undercut regions 18, 20.
The mould of
The removal of elements 92, 94, 96 causes the second and third up and away elements 98, 100 to move inwardly towards one another as represented by arrow 132, 134 in
Consequently, the parting lines are thus formed at locations on the surface of the component which do not obstruct use, or cause damage to a corresponding mating surface. Most advantageously, the moulding tool assembly results in a component having parting lines in favourable locations.
As an alternative to the
The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
Claims
1. A femoral component of a knee prosthesis, the component comprising a curved outer surface for bearing against a tibial component, the curved outer surface including a posterior end and an anterior end, the curved outer surface includes an area (A) which extends from a first position closer to the posterior end to a second position closer to the anterior end, wherein the area (A) includes no parting line.
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. The femoral component as claimed in claim 1, wherein the component includes an undercut region.
9. The femoral component as claimed in claim 8, wherein the undercut region is defined in a surface of the femoral component which faces in a direction which is opposite to the direction in which the outer surface faces.
10. The femoral component as claimed in claim 9, wherein the undercut region is arranged to define a cement pocket in the femoral component for retaining cement which may be used to facilitate securement of the femoral component to a femur during implantation.
11. The femoral component as claimed in claim 10, wherein the cement pocket has a depth of at least 0.5 mm.
12. The femoral component as claimed in claim 11, wherein the femoral component includes multiple undercut regions.
13. The femoral component as claimed in claim 12, wherein a series of ribs are provided in the surface of the femoral component which faces in a direction which is opposite to the direction in which the outer surface faces.
14. The femoral component as claimed in claim 13, wherein the ribs are equi-distantly spaced, preferably running parallel to one another.
15. The femoral component as claimed in claim 14, wherein the ribs run parallel to the flexion extension axis.
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. (canceled)
Type: Application
Filed: Jun 26, 2023
Publication Date: Oct 26, 2023
Inventors: Adam Briscoe (Thornton Cleveleys Lancashire), Ian Johns (Thornton Cleveleys Lancashire)
Application Number: 18/341,578